Question

Let X = {n ∈ N : 1 ≤ n ≤ 50}. If

A = {n ∈ X : n is multiple of 2} and

B = {n ∈ X : n is a multiple of 7}, then the number of elements in the smallest subset of X containing both A and B is_____

Answer 1

n(A) = 25

n(B) = 7

n(A ∩ B) = 3

n(A ∪ B) = 25 + 7 - 3 = 29